Thierry Kormann wrote (in http://lists.w3.org/Archives/Public/www-svg/2002Jan/0018.html)
>According to the SVG spec, if a mouse event occured on B or C, clientX and
>clientY should be relative to the viewport ([0, 0] [10000, 10000]) and this is
>not what the DOM spec says.
I went back and reread the thread again and caught this.
The example in my previous message should demonstrate that clientX and clientY are totally oblivious to the value of the viewBox attribute (at least for Adobe SVG Viewer), so clientX and clientY would not in the range ([0,0] to [10000,10000]), but in the device coordinate system of the user agent's window.